The present invention relates to shaped glass articles and more particularly it relates to channel-shaped glass articles and to devices for moulding shaped glass articles.
The present invention can be utilized in various branches of industrial and civil construction, in agriculture, and also for cultural and domestic applications where the employment of said articles in various structures ensures a required microclimate in buildings and gives them modern architectural outlines.
One of the most outstanding properties of glass consists in its ability to acquire a great variety of shapes in the course of moulding. Such various shapes can be produced by hot moulding when the glass melt is in a sufficiently soft state.
Among the physical and chemical properties of glass as a material the most conspicuous role belongs to viscosity and surface tension. The process of hot moulding in the glass industry consists of two stages, viz., producing a shape and fixing it. By cooling the glass melt to the required temperature it is possible to obtain any degree of plasticity which is best for the selected moulding method. For fixing the obtained shape, the articles are cooled still more to a temperature at which the glass melt loses the last traces of fluidity.
Thus, changes in the viscosity of glass melt in accordance with temperature changes in the course of moulding of glass articles is a decisive factor. In view of the fact that glass can have practically any degree of viscosity, it can be moulded by a diversity of methods.
Using such a factor as the reversibility of the law describing the dependence of the glass melt viscosity upon its temperature, one can resort to most complicated moulding methods wherein the glass melt being moulded comes repeatedly in contact with the elements of the moulding device.
The surface tension of glass in the automatic feeders of the modern glass-moulding machines is also an important factor since without the surface tension it would be impossible to impart the required shape to the glass melt fed into the moulding device.
Thus, the viscosity and surface tension of glass melt varying with the melt temperature create the specific favourable conditions for utilizing the various moulding methods used to produce the required shape of the glass articles.
The glass is moulded at relatively high temperatures, ranging from 700.degree. to 1000.degree. C. when the glass melt in the contact zone interacts with the elements of the material of the moulding devices, said elements exerting a serious influence upon the quality of the moulded articles.
From the viewpoint of technology and economy, the moulding devices must meet a number of requirements, viz., they must ensure a precise surface finish of the articles, be heat-resistant and thermostable, and possess adequate chemical stability, mechanical strength, hardness and durability. These requirements depend on the moulding method and the type of articles. Accordingly, the moulding elements are made of different materials; most frequently metal, ceramics or graphite.
While manufacturing industrial grades of glass the temperature of the moulding surfaces should not exceed 500.degree.-700.degree. C. However, the temperature of said surfaces should not be too low either since this leads to crystallization of glass and impairs the surface of the articles.
The term "moulding" as used in the glass industry covers all the processes in which the amorphous glass melt turns into a shaped article. These processes are divided into two consecutive stages, namely primary production and finishing.
The first stage includes all the processes wherein the glass melt is the source material and the product is constituted by a finished or a semifinished article.
The second stage includes processes in which the semifinished article obtained after primary production is given its final shape, its surface is improved, ornamented, etc.
Depending on its shape, size, glass thickness and other parameters, each glass article should be made by the most economical moulding method which ensures a maximum output of the technological equipment and a minimum production cost of the article.
At present, the glass moulding methods can be divided into five major groups, viz., pressing, blowing, pressing-and-blowing, drawing, and rolling. In addition, there also is a casting method and the so-called mollification wherein the glass is reheated to a soft state and the viscosity of the glass melt is very high.
Glass articles are available in a great variety of shapes and sizes and are widely employed in various branches of industry. For example, shaped glass articles are used in the construction and erection of different elements of buildings and structures, viz., outer and inner walls, roofing, lining, light apertures, window sashes, door casings, etc.
The shaped glass articles can be channel-shaped, box-shaped, U-shaped, Z-shaped, semicircular, etc. A rich assortment of architectural and construction glass articles dictates serious differences in the technical requirements for each type of articles, in their production methods and in the composition of glass melts used for their production.
The shaped glass articles are made of ordinary alkaline and low-alkaline glass.
Of late, the shaped glass articles began to be used in agriculture for construction of hothouses and hotbeds in which the ceilings and walls are made of channel-shaped glass articles. In making glass blocks from these articles, the latter are joined with the aid of various sealing gaskets. However, unreliable sealing of these joints has checked wide employment of the shaped glass articles in various branches of construction.
The use of channel-shaped glass articles in various branches of construction aids in solving important engineering problems. It is known that the glass articles used in construction must meet the following requirements:
sufficient strength for sustaining mechanical loads; PA1 heat-insulating ability equivalent to that of glass windows; PA1 sound-proofing ability, i.e. acoustic requirements; PA1 increase the light area of windows by dispensing with window sashes which is an important factor in industrial and agricultural construction; PA1 produce dissipating light, i.e. distribute uniformly the light fluxes inside the buildings; PA1 ensure reliable sealing between the elements of the glass articles and between the building structures which is necessary for creating a certain microclimate inside the glazed buildings; PA1 produce a modern appearance of the building; PA1 reduce the amount of wood utilized in window sashes and of labour involved in making and installing said sashes.
Known in the previous art are devices for moulding channel-shaped glass articles comprising elements for moulding straight flanges. The moulding device consists of plates arranged one above the other, each plate being provided with two elements shaped like a rectangular bar. Leaving the rolls, the glass strip enters the moulding device wherein two straight flanges of the shaped article are moulded with the aid of said two elements shaped like a rectangular bar.
However, the device of this type fails to produce glass articles which can be reliably sealed at the joints, this being an important factor in assembling a glass block from a multitude of such articles.
Also known in the art are moulding devices for making shaped glass articles, said devices consisting of two plates arranged one above the other; the lower plate is provided with wedge-like projections whereas the upper one has calibrating slots located above the projections of the lower plate. Located on the lower plate are two elements shaped like rectangular bars. The glass strip discharged from the rolls enters the moulding device. The wedge-like projections of the lower plate form stiffener ribs on the strip while the slots in the upper plate ensure calibration of said ribs. The straight flanges of the shaped article are bent by two elements in the form of rectangular bars.
This devices ensures additional mechanical strength of the moulded articles by providing them with stiffener ribs. However, this device too cannot produce glass articles which, being assembled into a block, would be reliably sealed at the joints between the individual elements.